Asian soybean rust finding confirmed in south Louisiana kudzu

The LSU AgCenter announced Asian soybean rust had been found in a Louisiana kudzu patch south of Lafayette near New Iberia on June 30. As of July 7, the disease has not spread.

“Late on June 29, Blaine Viator reported he’d found something that looked a lot like ASR,” said David Lanclos, LSU AgCenter soybean specialist, shortly after the disease confirmation. “Along with several sentinel plots, Blaine has been monitoring that kudzu for a while. When he found this suspicious patch he gave us a call. He drove a sample to Baton Rouge this morning.”

After having a look, plant pathologists said Viator’s initial ASR diagnosis was correct. The diagnosis was further confirmed on July 7 when a Florida lab released PCR test results on the samples showing ASR.

Viator, a prominent sugarcane consultant in south-central Louisiana, found the infected kudzu in a low-lying area beneath a tree. That region has been receiving intermittent showers so there was moisture available to the disease.

Since the find, “everyone has been beating the bushes,” said Lanclos. “But out from under that tree nothing has been found. That’s fantastic news.”

The infection on the leaves Viator brought to LSU was “very heavy,” said Ray Schneider, LSU AgCenter research plant pathologist on July 7. “To me, that suggests that there had been a substantial spore shower probably, about, three weeks ago. The innoculum is blowing in from somewhere – perhaps Texas or Mexico. Spores are arriving and have been for some time.”

Does Louisiana have the conditions favorable for disease development?

“Certainly, for the past few, rainy days, we have. However, even if infection has occurred in the last few days, ASR won’t show up on leaves for the next 10 days, or so. And that’s at the earliest.”

The Florida lab results come after a week of rains across parts of Louisiana.

“We got some rain this week and thank God for it,” said Lanclos on July 7. “It will probably help finish the bulk of our soybean crop. These rains should help the advanced crop fill out adequately. I hope that’s the case because the long-term forecasts say it’s about to turn very dry again.”

The rain was extremely variable across the state.

“In some areas, water is standing in ditches and in other areas dust devils are flying in the fields. Regardless, you’d have to be completely ignorant of ASR pathology if you didn’t think this doesn’t present a better chance for the disease to pick up and go.”

Between 50 and 60 percent of the state’s soybeans are already at R-5.

“The cutoff for ASR, according to everything we know – and we are still on a learning curve – is once we get to R-6 there’s no real harm ASR can do to the crop. So we’re about two weeks away from being able to say 60 percent of our crop is safe.”

As for recommendations, “we’re not changing course just because of this kudzu patch. If it’s found in soybeans and appears to be spreading, then we’ll definitely change our tune.

“We’re not promoting not spraying. We’re just suggesting producers stay on the spraying program they’re normally on. If they’re not ones for any risk, they can add a triazole to the system. That might help some folks sleep better.”

Those in the field will be keeping a very close eye on the crop, said Schneider.

“If we find ASR in the next couple of weeks coupled with any rain, I’d say the risk is high for rapid disease development. We’re still at risk. There’s no reason to underestimate this disease. Last year, the ASR outbreaks in Florida and Georgia were as bad as those in Brazil. In Louisiana, if things line up, we could easily see the same.”